Modern mobile communications tend to provide users with high-speed multimedia services. As shown by FIG. 1, it is a system architecture schematic diagram of System Architecture Evolution (SAE), wherein
User Equipment (UE) 101 is a terminal device for receiving data. Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102 is a wireless access network, comprising macro base station (eNodeB/NodeB) that provides UE with wireless network interface. Mobile Management Entity (MME) 103 is in charge of mobile context, session context and security information of UE. Service Gateway (SGW) 104 mainly serves to provide a user plane, where MME 103 and SGW 104 may be in the same physical entity. Packet Data Network Gateway (PGW) 105 is in charge of duties such as billing, lawful interception, etc., which may also be in the same physical entity with SGW 104. Policy and Charging Rules Function (PCRF) 106 provides quality of service (QoS) policies and charging rules. Serving GPRS Support Node (SGSN) 108 is a network node equipment in the Universal Mobile Telecommunications System (UMTS) that provides routing for data transmission. Home Subscriber Server (HSS) 109 is the home subsystem of UE, which is in charge of user information including the current location of the user equipment, address of service node, security information about the user, package data context of the user equipment, etc.
3GPP proposes in Edition 12 (Rel-12) a requirement for small cell enhancement. Target scenarios for small cell enhancement include: a scenario under coverage of macro cells and scenarios without coverage of macro cells, indoor and outdoor, ideal and nonideal backhaul enhancement, as shown by FIG. 2.
In the condition under the coverage of macro cells, the application of the technique of carrier aggregation between base stations is put forward. Macro cells and small cells may operate in different frequency bands. However, technical solution of how to enhance performances of small cells are still absent in the condition not covered by macro cells.